Recently, there has been considerable interest within the detergent industry for laundry detergents which have the convenience, aesthetics and solubility of liquid laundry detergent products, but retain the cleaning performance and cost of granular detergent products. The problems, however, associated with past granular detergent compositions with regard to aesthetics, solubility and user convenience are formidable. Such problems have been exacerbated by the advent of “compact” or low dosage granular detergent products which typically do not dissolve in washing solutions as well as their liquid laundry detergent counterparts. These low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers prior to use, but less convenient upon dispensing into the washing machine as compared to liquid laundry detergent which can be simply poured directly from the bottle as opposed to “scooped” from the box and then dispensed into the washing solution.
Granular detergent products are typically produced from one of two manufacturing methods. The first involves the spray-drying of a aqueous detergent slurry in a spray drying tower to produce detergent granules while the second involves dry mixing various components after which they are agglomerated with a binder such as surfactant. The resultant detergent particles are then dried to achieve an acceptable moisture content such that the finished product is flowable and non-caking in the package once delivered to the consumer. In both processes, the factors which impact these flow characteristics include chemical composition and type and length in the drying process.
Many surfactant materials included in granular detergents, including linear alkyl benzene sulfonates (“LAS”), ethoxylated alkyl sulfates and nonionic surfactants, tend to be relatively “sticky” in nature, difficult to fully dry and lead to lumping, caking and flowability problems in the finished product. Accordingly, there exists a need to reduce the flowability problems associated with these “sticky” surfactants in finished detergent products.
In addition, detergent processes in which inorganic materials are incorporated into the process are well known. For example, U.S. Pat. No. 5,576,285 discloses the use of inorganic double salts as dry mix ingredients in an agglomeration process as well as the dry coating of aluminosilicates, carbonates and silicates as flow control agents. In these processes, the coating material is applied as a dry ingredient and merely dusts or sticks to the outside of the particles rather than as a true coating adhering to the particle itself. This patent also discloses the spraying of liquid binder materials such as water, surfactants, polymers, etc. into the mixers or fluid bed of a detergent process. Additional patents teach spraying various materials including alkali metal silicates and surfactants into a detergent making process including PCT applications WO97/22685 and WO99/00475 and German patent application DE 4435743. However, in the case of silicate coatings, the hygroscopic nature of the silicate can lead to moisture uptake during storage of the detergent, especially in humid conditions; moisture adsorption results in caking and lumping of the detergent powder, causing poor scoop and flow properties and degraded aesthetics of the product.
Accordingly, the need remains for a process which can produce a detergent granule having improved flow properties and aesthetics and which may be included in detergent compositions.